This invention relates to a recording/reproducing device for recording and reproducing data on and from a recording medium through a read/write head and, in particular, to a recording/reproducing mechanism for driving a carriage assembly with the read/write head mounted thereon by a voice coil motor in a predetermined direction relative to the recording medium.
As a typical one of such a recording/reproducing device, there is well known in the prior art a disk drive for recording and reproducing data on and from a magnetic recording medium by a magnetic head. The magnetic recording medium is a so called flexible disk and is usually housed in a hard case or a cartridge. The cartridge containing the flexible disk is called a floppy disk. In recent years, the storage capacity of the flexible disk has increased. Development has been made of those flexible disks having a storage capacity as large as 128 megabytes in contrast with those having a storage capacity on the order between one and two megabytes. The former and the latter flexible disks will hereafter be referred to as large-capacity flexible and normal-capacity flexible disks, respectively. Following such remarkable increase in storage capacity, an improved disk drive has also been developed so as to deal with the large-capacity flexible disks.
The disk drive for use with the normal-capacity flexible disks is different in mechanism from that intended for use with the large-capacity flexible disks. One such difference lies in the structure of a driving mechanism for driving a carriage assembly with a magnetic head relative to the flexible disk received in the disk drive. More specifically, the disk drive for the normal-capacity flexible disks uses a stepping motor as the driving mechanism. On the other hand, the disk drive for the large-capacity flexible disks uses a linear motor such as a voice coil motor (VCM).
The carriage assembly is moved in a carriage moving direction which is a predetermined radial direction of the flexible disk.
The voice coil motor used as the driving mechanism in the disk drive for the large-capacity flexible disks comprises a pair of voice coils fixedly mounted on both sides of the carriage assembly each having a coil axis arranged in the carriage moving direction, and a pair of magnetic circuit devices fixedly disposed adjacent the voice coils, respectively, each for generating a magnetic field in a direction intersecting an electric current flowing through each of the voice coils.
Each of the magnetic circuit devices typically comprises a permanent magnet polarized along its thickness, and a yoke member. The yoke member comprises a center yoke, a back yoke, and a pair of side yokes. The center yoke extends in the carriage moving direction and passes through the corresponding one of the voice coils along the coil axis. The back yoke extends in parallel to the center yoke at a certain distance therefrom and has a principal surface faced to the center yoke. The side yokes connect the center yoke with the back yoke at their one ends and the other ends to establish an endless form. The permanent magnet is fixedly attached to the principal surface of the back yoke. Each of the center yoke, the back yoke, and the side yokes is made of a steel plate having a thickness of at least 3 mm.
The magnetic circuit device produces the magnetic field across a space between the center yoke and the back yoke. The electric current flows through the voice coil in a direction intersecting the magnetic field. The interaction between the electric current and the magnetic field produces a driving force to drive the voice coil in the carriage moving direction along the center yoke. In this manner, the carriage assembly is moved in the carriage moving direction in response to the driving force of the voice coil motor.
Thus, a combination of the voice coil motor and the carriage assembly serves as a magnetic recording/reproducing mechanism in the disk drive.
In the above-mentioned magnetic recording/reproducing mechanism, the magnetic circuit device of the voice coil motor comprises the yoke member composed of the center yoke, the back yoke, and the side yokes. Thus, the yoke member includes a relatively large number of components.
In the magnetic circuit device, the permanent magnet, the center yoke, the back yoke, and the side yokes are equal in width to one another. As described above, the voice coil motor produces the driving force by the interaction between the electric current flowing through the voice coil and the magnetic field produced by the magnetic circuit device. The intensity of the driving force depends on the magnitude of the electric current and the number of magnetic fluxes intersecting the voice coil. In order to increase the driving force, it is necessary either to increase the electric current flowing through the voice coil or to increase the number of the magnetic fluxes across the voice coil. However, the electric current to flow through the voice coil is limited in magnitude.
On the other hand, the magnetic field intersecting the voice coil, i.e., the number of the magnetic fluxes can be increased if the permanent magnet is made of an advanced magnetic material or if the permanent magnet, the center yoke, the back yoke, and the side yokes are increased in width. However, the use of the permanent magnet made of such an advanced magnetic material will increase the cost of the voice coil motor because the advanced magnetic material is expensive. On the other hand, the increase in width of the permanent magnet, the center yoke, the back yoke, and the side yokes inevitably increases the size and the weight of the voice coil motor.
In the disk drive, it is a general practice that the voice coil is fixed to a side wall of the carriage assembly by the use of an adhesive.
However, it is difficult to fix the voice coil to the carriage assembly with an accurate position. Furthermore, the voice coil is often disconnected or released from the carriage assembly because of deterioration of the adhesive resulting from various factors, such as generation of heat within the device and the lapse of time.